Purpose:In studies related to breast cancer and mortality, convincing evidence of an increased risk of cardiac morbidity following irradiation for leftsided breast cancer exists. The use of a breath hold technique enables a significant decrease of the dose to the heart as well as to the left anterior descending coronary artery (LAD). The purpose of deep inspiration Breath Hold (BH) is to expand the chest cavity during radiotherapy, which increases the distance between the breast to be treated and the heart. This allows for a lower heart dose as well as better PTV coverage.Methods:A study of 30 patients is showed. All patients underwent a free breathing (FB) and BH CT scan in supine treatment. Previously, the patient receives personal training to perform an adequate breathing and follows her own breathing cycle with glasses connected to the BH device. For simulation and treatment the same procedure as in the CT acquisition is performed. In the treatment, the patient placing includes daily image included in dosimetry.Results:The analysis compares the doses received in heart and LAD with FB and BH treatment. It presents data of medium dose with FB CT and BH CT and average and maximum dose (dose to 0.2 cm3) in LAD. The PTV coverage dose are between 95-107 percentage of the prescribed dose is not present neither in the lung dose (V20) does not vary significantly.The DVH medium of LAD and heart (FB vs BH) is showed as well.Conclusion:The effects of radiation on the heart are late effects, which usually appear between 10 and 15 years after treatment. In young patients a dose reduction as drastic as that observed implies a reduced risk of heart disease a result of radiation, which significantly increases the probability of survival over 10 years.